1. Field of the Invention
The present invention relates to refrigerated chambers or boxes of the type comprising an insulated chamber and an associated compression-type refrigeration system including an electrically-driven compressor, refrigerant conduit means, evaporator means contained within said chamber, one or more evaporator fans contained within said chamber, and thermostatic switch means contained within said chamber for controlling the operation of said compressor or the recirculation of said refrigerant, and more particularly to energy conservation methods and devices for operating said evaporator fan or fans at a high speed when said thermostatic switch means is in a first state and for operating said evaporator fan or fans at a low speed when said thermostatic switch means is in a second state.
2. Description of the Prior Art
It is known in the prior art to provide compression refrigeration systems for refrigerated chambers with control means for control ling the speed of the evaporator fan or fans thereof in accordance with some sub-system condition, such as the operating state of the compressor motor. For example, U.S. Pat. No. 3,877,243, issued to Daniel E. Kramer on Apr. 15, 1975, discloses a refrigeration system having a compressor driven by a motor having a control for turning it on and off, and an evaporator which includes a motor-driven fan where the fan motor can operate at high speed or at low speed, and where the fan motor is connected to operate at high speed when the compressor motor is on and to operate at low speed when the compressor motor is off.
The low speed fan energizing voltage for single speed evaporator fan motors in Kramer is obtained by either (a) connecting the fan motor or fan motors between the neutral connection and one leg of a three-phase power source, or (b) connecting a reactor or choke in parallel connection with a relay in series with each evaporator fan motor.
The three-phase embodiment (a) of Kramer suffers from the disadvantage that in many existing installations the compressor is remote from the insulated chamber and thus the retrofitting of an evaporator fan motor controller of the type used in Kramer would, in many cases, require the provision of a substantial amount of new wiring.
Further, as is well known to those having ordinary skill in the art, very few compression-type refrigeration systems used in connection with refrigerated chambers energize the evaporator fan motor or motors with three-phase power, and thus the three-phase embodiment of Kramer is applicable to only a few compression-type refrigeration systems used in connection with refrigerated chambers.
Yet further, since a vast majority of such refrigeration systems comprise 120-volt evaporator fan motors, the three-phase embodiment of Kramer is applicable to only a small minority of refrigerated chambers.
The reactor embodiment (b) of Kramer suffers from the disadvantage that the reactor or choke connected in series with each evaporator fan motor in a particular system must be selected in accordance with the characteristics of that fan motor, thereby requiring the installer to have knowledge of Ohm's Law for alternating current circuits, which knowledge many installers lack, and, in the event that reactors of suitable inductance are not available, necessitating the winding of special reactors.
Further, the evaporator fan motor control system of Kramer suffers from the disadvantage that its operation is not failsafe when the coil of the relay connected across the compressor motor control relay coil fails. More particularly, when in the system of Kramer the relay coil 88 fails to function, i.e., to draw armature 84 against the urging of spring 86, the evaporator fans operate continuously at low speed, causing the evaporator to freeze up. Since, in this condition, no heat is exchanged, the refrigerant remains in a liquid state and is returned in a liquid state to the compressor via the suction line. The liquid refrigerant, upon reaching the compressor, is very likely to destroy the compressor due to the incompressibility thereof.
U.S. Pat. No. 4,485,633, issued to Eddie W. King and Robert D. Hughes on Dec. 4, 1984, (hereinafter "King") discloses a compression-type refrigeration system for chilled-product vending machines.
The system of King includes a temperature-based responsive control circuit including a product sensor for detecting the temperature of the chilled products and cycling the evaporator fan on in response to detected product temperatures above a predetermined limit, the predetermined limit being less than the temperature required to turn the compressor on, and a coil sensor for detecting the temperature below a predetermined limit, maintaining said evaporator fan on during and beyond the end of the compressor cycle, and cycling the evaporator fan off when the temperature of the coil stabilizes above the freezing point of water.
The King system suffers from the disadvantage that it requires the addition of two temperature sensors in the evaporator fan motor circuit, such as are not normally found in compression-type refrigeration systems for refrigerated chambers, thus increasing the cost and complexity of the control system of King.
Further, the evaporator fan motors are completely turned off during certain phases of the operating cycle of the system of King, thus raising the possibility that the air in the refrigerated space of the device of King may become stratified, and also raising the possibility that, in the absence of the heat provided by running fan motors, the temperature within the chamber may drop below the thermostatically set temperature when the temperature outside the insulated chamber is colder than the thermostatically set temperature. In this condition the grease in the evaporator fan motor bearings may stiffen to such an extent that the fan motors may not restart, resulting in fan motor winding burnout due to lack of counter electromotive force.
U.S. Pat. No. 4,467,617, issued to Annis R. Morgan, Jr., and Eddie W. King on Aug. 28, 1984, discloses a compression-type refrigeration system for chilled-product vending machines which is similar in many ways to the system of the above-discussed King patent, except that the on and off cycling of the evaporator fan motors is accomplished by timing devices, rather than by temperature sensitive devices.
In general, then, the disadvantages of the King device, as discussed hereinabove, are also characteristic of the device of the Morgan and King patent.
It is believed that the documents listed immediately below contain information which might be considered to be material to the examination hereof.
U.S. Pat. No. 3,070,972 PA1 U.S. Pat. No. 3,398,889 PA1 U.S. Pat. No. 3,505,828 PA1 U.S. Pat. No. 3,514,967 PA1 U.S. Pat. No. 3,517,523 PA1 U.S. Pat. No. 4,109,482 PA1 U.S. Pat. No. 4,167,966 PA1 U.S. Pat. No. 4,673,850 PA1 Japanese Patent No. 57-21739 PA1 Japanese Patent No. 56-151826
It is to be understood that the term "prior art" as used herein or in any statement made by or on behalf of applicants means only that any document or thing referred to as prior art bears, directly or inferentially, a date which is earlier than the effective filing date hereof.
No representation or admission is made that any of the above-listed documents is part of the prior art, or that an exhaustive search has been made, or that no more pertinent information exists.
A copy of each of the above-listed documents is supplied to the United States Patent and Trademark Office herewith.